This invention relates to a process for the preparation of phloroglucinol.
Several processes for making phloroglucinol are already known. In particular, the reduction of 1,3,5-trinitrobenzene to 1,3,5-triaminobenzene and its subsequent hydrolysis to form phloroglucinol is industrially important. According to older processes, the reduction step may be accomplished by utilizing tin in hydrochloric solution (Weidel and Pollak, Monatsh. 21, 15, (1900); Hepp. Ann. 215, 348; Organic Synthesis Coll. Vol. I, 444 (1932); U.S. Pat. No. 2,461,498), or with hydrogen and Raney nickel in an organic solvent, such as ethyl acetate (German Pat. No. 813,709; Gill et al., J. Chem. Soc. 1753 (1949); British Pat. No. 1,106,088). A reducing agent suitable for the large-scale industrial reduction of the trinitrobenzene is iron/hydrochloric acid (U.S. Pat. No. 2,614,126; Kastens, Ind. and Engin. Chem. 42, 402 (1950); British Pat. No. 1,022,733). Platinum, palladium and rhodium catalysts have also been proposed for the reduction of trinitrobenzene (French Pat. No. 1,289,647; Desseigne, Mem. Poudres 44, 325 (1962). In such a synthesis, instead of starting with 1,3,5-trinitrobenzene, one can also start with 2,4,6-trinitrobenzoic acid, which on a large scale is obtainable through the oxidation of trinitrotoluene with sodium dichromate in sulfuric acid (Kastens, 1.c.), since the 2,4,6-triaminobenzoic acid formed in the reduction either decarboxylates immediately to triaminobenzene, or is converted to phloroglucinol during the subsequent hydrolysis (British Pat. Nos. 1,022,733; 1,106,088; 1,274,551). Furthermore, it is known to start with 5-nitro-1,3-diaminobenzene instead of trinitrobenzene (British Pat. No. 1,012,782. The hydrolysis of the triamine to phloroglucinol is customarily carried out in a mineral acid solution (Flesch, Monatsh. 18,755 (1897); German Pat. No. 102,358, or, according to a more recent process, in the presence of copper and/or its salts as catalysts (German Pat. No. 1,195,327).
According to a process likewise of interest from an industrial viewpoint, one may obtain phloroglucinol by oxidizing 1,3,5-triisopropyl benzene, separating the trihydroperoxide from the resulting mixture of mono-, di- and trihydroperoxides, and subjecting it subsequently to ketone splitting (British Pat. No. 751,598; German Pat. No. 12,239; Seidel et al., Journ. prakt. Chemie 275, 278 (1956). It is also possible to convert triisopropyl benzene directly to phloroglucinol triacetate through oxidation with oxygen in acetic anhydride, followed by hydrolysis with alcoholic sodium hydroxide to form phloroglucinol. One may also start with m-isopropyl resorcinol, which is esterified with acetic anhydride; the resulting m-isopropyl resorcinol diacetate is then oxidized to hydroperoxide and the latter is finally converted to phloroglucinol with acid (U.S. Pat. No. 3,028,410). Phloroglucinol may also be obtained, if resorcinol (Barth and Schreder, Ber. 12, 503, (1879), resorcinol substituted in 2-, 4-, 5-, 3,5- or 2,4-position by chlorine or bromine (German Pat. No. 2,231,005), or 1,3,5-benzene trisulfonic acid (U.S. Pat. No. 2,773,908) are melted with excess alkali hydroxide.
In addition to the listed benzene derivatives, mention has also been made of hexahydroxybenzene, picryl chloride, tetrachloro- and tetrabromobenzene, as well as tribromobenzene, as initial materials for phloroglucinol synthesis. Hexahydroxybenzene may be hydrated with platinum oxide in an aqueous medium (Kuhn et al., Ann. 565, 1 (1949), picryl chloride may be reduced with tin and hydrochloric acid, or electrolytically, and the 1,3,5-triaminobenzene, or 2,4,6-triamino-1-chlorobenzene obtained thereby may then be hydrolyzed (Heertjes, Recueil 78, 452 (1959).
The above-mentioned tetrahalobenzenes may be subjected to ammonolysis in the presence of a copper catalyst and the intermediary triamine may be hydrolyzed in the reaction mixture without a preceding separation (U.S. Pat. No. 3,230,266). Tribromobenzene may be converted to 1,3,5-trimethoxybenzene with sodium methanolate and catalytic quantities of copper iodide in methanol/dimethyl formamide as a solvent, and also may be subsequently subjected to hydrolysis (McKillop et al., Synthetic Communications 4 (1) 43,35 (1974).
Reference may also be made to the process of German Patent Disclosure No. 2,362,694, according to which 2,6-, 2,4-, 2,5-, or 3,5-dihalogen phenols dissolved in pseudo-cumene are heated in the presence of a strong alkali.
Furthermore, there is also a known phloroglucinol synthesis based on diethyl malonate. When subjected to treatment with metallic sodium, the malonic diethyl ester may condense with itself to form the trisodium salt of phloroglucinol dicarboxylic diethyl ester and this intermediate product may then be subjected to alkaline hydrolysis and decarboxylation (v. Baeyer, Ber. 18, 3454 (1885); Willstaetter, Ber. 32, 1272 (1899); Leuchs, Ber. 41, 3172 (1908); Komninos, Bull. Soc. Chem. Fr. 23, 449 (1918). Such a synthesis has been improved to the extent that the formation of the sodium malonic diethyl ester and the trisodium salt of phloroglucinol dicarboxylic diethyl ester may be performed in a single operation by means of boiling in an inert, high-boiling solvent, preferably dekalin (East German Pat. No. 24,998).
From the above-mentioned processes, apparently only the process based upon 2,4,5-trinitrobenzoic acid has been utilized commercially. However, such a process has several serious drawbacks. 2,4,5-trinitrobenzoic acid may be prepared by oxidizing trinitrotoluene, which is explosive, thus rendering such a process dangerous. In addition, the total yield, measured on the basis of 2,4,6-trinitrobenzene, of phloroglucinol produced via the intermediates of trinitrobenzene and triaminobenzene, is low. Such a process is also disadvantageous because the waste water formed during the oxidation and reduction is strongly acid and contains the heavy metals chromium and iron, and must therefore be treated.
Very recently, two additional technical synthesis of phloroglucinol have been discovered. According to the process disclosed in U.S. Pat. No. 4,123,461, benzene-tricarboxylic acid-(1,3,5)-triamide is chlorinated in an aqueous mineral acid medium, the resulting benzene-tricarboxylic acid-(1,3,5)-tri-N-chloramide, upon treatment with ammonium, is converted to 1,3,5-triureido benzene, and the latter compound subsequently hydrolyzed in a mineral acid solution. According to the process disclosed in U.S. Pat. No. 4,071,555, s-triacetyl benzene is converted into benzene-1,3,5-trisacetoxime, which is subjected to a Beckmann rearrangement, whereupon the resulting mixture and substances are subjected to acid hydrolysis. In both of the latter processes the initial materials are easily accessible, the yields are high, and pure products are obtained.